U.S. patent application number 15/026062 was filed with the patent office on 2016-08-18 for system and method for myocardial perfusion pathology characterization.
The applicant listed for this patent is King's College London, Koninklijke Philips N.V.. Invention is credited to Marcel BREEUWER, Amedeo CHIRIBIRI, Eike NAGEL.
Application Number | 20160235330 15/026062 |
Document ID | / |
Family ID | 49322196 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160235330 |
Kind Code |
A1 |
BREEUWER; Marcel ; et
al. |
August 18, 2016 |
SYSTEM AND METHOD FOR MYOCARDIAL PERFUSION PATHOLOGY
CHARACTERIZATION
Abstract
A method of characterizing myocardial perfusion pathology by
analyzing a plurality of medical images of at least a portion of
the heart of a subject of interest (20), acquired in a consecutive
manner by a medical imaging modality (10), the method comprising
steps of: sampling intensities of selected myocardial image
positions from the plurality of medical images and assigning an
index representing an order of acquisition to the respective
sampled intensities of the myocardial image positions to obtain
intensity curves (60); and--calculating an index number (64, 66)
indicative of a spatio-temporal perfusion inhomogeneity or
perfusion dephasing among at least a subset of myocardial segments
of the plurality of myocardial segments, based on the obtained
intensity curves (60); a system (52) for myocardial perfusion
pathology characterization by analyzing a plurality of medical
images by carrying out such method; a medical imaging modality (10)
comprising such system (52); a software module (48) for carrying
out such method.
Inventors: |
BREEUWER; Marcel;
(Eindhoven, NL) ; CHIRIBIRI; Amedeo; (Eindhoven,
NL) ; NAGEL; Eike; (Eindhoven, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Koninklijke Philips N.V.
King's College London |
Eindhoven
London |
|
NL
GB |
|
|
Family ID: |
49322196 |
Appl. No.: |
15/026062 |
Filed: |
October 1, 2014 |
PCT Filed: |
October 1, 2014 |
PCT NO: |
PCT/EP2014/071109 |
371 Date: |
March 30, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 6/032 20130101;
A61B 6/503 20130101; A61B 5/0044 20130101; A61B 5/04017 20130101;
A61B 5/0402 20130101; A61B 6/481 20130101; A61B 6/037 20130101;
A61B 6/507 20130101; G06T 2207/10076 20130101; A61B 8/481 20130101;
A61B 8/0883 20130101; G06T 7/0016 20130101; G01R 33/5608 20130101;
A61B 8/06 20130101; G06T 2207/30048 20130101; G01R 33/56366
20130101; A61B 5/026 20130101; A61B 5/055 20130101; G06T 2207/30104
20130101 |
International
Class: |
A61B 5/055 20060101
A61B005/055; A61B 5/026 20060101 A61B005/026; A61B 5/00 20060101
A61B005/00; G01R 33/563 20060101 G01R033/563; A61B 5/04 20060101
A61B005/04; A61B 8/06 20060101 A61B008/06; A61B 8/08 20060101
A61B008/08; A61B 6/03 20060101 A61B006/03; A61B 6/00 20060101
A61B006/00; A61B 5/0402 20060101 A61B005/0402 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2013 |
EP |
13186934.9 |
Claims
1. A method of characterizing myocardial perfusion pathology by
analyzing a plurality of medical images of at least a portion of
the heart of a subject of interest, the plurality of medical images
being acquired in a consecutive manner by a medical imaging
modality, the method comprising steps of: delineating contours of a
selected part of the heart of the subject of interest in the
plurality of medical images and segmenting the selected part into a
plurality of segments; sampling intensities of selected myocardial
image positions from the plurality of medical images and assigning
an index representing an order of acquisition of each one of the
medical images to the respective sampled intensities of the
myocardial image positions to obtain intensity curves for each of
the selected myocardial image positions; calculating an index
number indicative of a spatio-temporal perfusion inhomogeneity or
perfusion dephasing among at least a subset of myocardial segments
of the plurality of myocardial segments, wherein the subset of
myocardial segments includes a plurality of myocardial segments,
based on the obtained intensity curves.
2. The method as claimed in claim 1, further comprising a step of
conducting quantification of myocardial blood flow in each segment
of the plurality of segments.
3. The method as claimed in claim 1, wherein the plurality of
medical images is acquired by the medical imaging modality after
administering a contrast agent to the subject of interest.
4. The method as claimed in claim 1, further comprising a step of
identifying a reference location in the selected part of the heart,
wherein in the step of calculating the index number, the intensity
curves are evaluated with reference to a reference time that is
determined by the identified reference location.
5. The method as claimed in claim 4, further comprising a step of
automatically determining, for each of the selected myocardial
positions, an individual time period (TTPI) relative to a reference
time that is determined by the identified reference location, until
an occurrence of a characteristic feature of the sampled intensity
of each of the myocardial image positions, wherein the individual
time periods (TTPI) are used in the step of calculating the index
number.
6. The method as claimed in claim 4, wherein the step of
calculating the index number comprises a calculation of a
statistical measure that is indicative of a variation of the time
(TTPI) until occurrence of the characteristic feature at each of
the individual myocardial positions relative to the time of
occurrence of the characteristic feature at the identified
reference location.
7. The method as claimed in claim 1, wherein the acquiring of the
plurality of medical images of at least a portion of the heart of
the subject of interest is at least partially synchronized to a
cyclic movement of the heart of the subject of interest.
8. The method as claimed in claim 1, wherein in the step of
sampling intensities of myocardial image positions, the myocardial
image positions are selected in a direction along the myocardium as
well as in a direction across the myocardium.
9. The method as claimed in claim 1, further comprising a step of
generating a perfusogram and displaying it to a user.
10. The method as claimed in claim 1, further comprising a step of
implementing at least one marker in the perfusogram that is
indicative of at least one characteristic position and/or at least
one characteristic point in time.
11. The method as claimed in claim 1, further comprising a step of
implementing a plurality of computer links, wherein each computer
link of the plurality of computer links is assigned to a location
in the perfusogram, and wherein each computer link of the plurality
of computer links is linked to a data set representing a medical
image of the plurality of medical images.
12. A system for myocardial perfusion pathology characterization by
analyzing a plurality of medical images of at least a portion of
the heart of a subject of interest, the plurality of medical images
being acquired in a consecutive manner by a medical imaging
modality, the system comprising a delineation unit, provided for
delineating contours of a selected part of the heart of the subject
of interest in the plurality of medical images and for segmenting
the selected part into a plurality of segments; an intensity
sampler and analyzing unit configured for sampling intensities of
myocardial image positions from the plurality of medical images and
assigning an index representing an order of acquisition of each one
of the medical images to the respective sampled intensities of the
myocardial image positions; and for calculating an index number
indicative of a spatio-temporal perfusion inhomogeneity or
perfusion dephasing among at least a subset of myocardial segments
of the plurality of myocardial segments.
13. A medical imaging modality comprising the system as claimed in
claim 12.
14. The medical imaging modality as claimed in claim 13, designed
as a magnetic resonance imaging apparatus.
15. A software module for carrying out a method as claimed in claim
1 of characterizing myocardial perfusion pathology, wherein the
method steps to be conducted are converted into a program code of
the software module, wherein the program code is implementable in a
memory unit of a control unit of the medical imaging modality and
is executable by a processor unit of the control unit of the
medical imaging modality.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the field of medical imaging of the
heart, and in particular to the field of analyzing medical images
of the heart.
BACKGROUND OF THE INVENTION
[0002] First-pass enhancement imaging of the heart by cardiac
magnetic resonance (CMR) imaging, and more recently also cardiac
computed tomography (CCT) imaging, allows for quantification of
myocardial perfusion. This quantification includes
semi-quantitative or true quantitative analysis of time-intensity
curves. Semi-quantitative analysis comprises quantification of
several characteristic features of time-intensity curves, for
instance peak intensity, maximum upslope, mean transit time, and
others. In true quantitative analysis, the actual myocardial blood
flow is calculated from a mathematical analysis of the arterial
input function (AIF) and the time-intensity curves obtained in the
myocardium. An extensive review of both semi-quantitative and true
quantitative approaches is given in Jerosch-Herold: Quantification
of myocardial perfusion by cardiovascular magnetic resonance,
Journal of Cardiovascular Magnetic Resonance 2010, 12:57.
[0003] International application WO 2005/004066 A1 describes a
method for quantitative assessment of cardiac perfusion. The method
includes dividing a myocardium that is depicted on a series of
cardiac images into image segments comprising at least one image
pixel and determining a cardiac perfusion parameter for each of the
image segments. Further, at least one image segment with a normal
perfusion parameter value is selected, and subsequently, cardiac
perfusion parameters of the remaining image segments are based on
the normal perfusion parameter value. In one embodiment, the
perfusion parameter is a maximum upslope of a time-intensity
profile for distribution of a contrast agent in the myocardium. A
normal maximum upslope is derived for at least one image segment
and a relative maximum upslope is calculated for each segment with
relation to the normal maximum upslope. Based on these values, a
ratio of myocardial perfusion parameters derived at stress and
myocardial perfusion parameters derived at rest is calculated for
each segment. As an example, it is described to calculate a
myocardial perfusion reserve index (MPRI) for each segment, defined
as a ratio of the relative maximum upslopes derived at rest and at
stress.
SUMMARY OF THE INVENTION
[0004] At present, myocardial perfusion deficits exist that require
an application of invasive methods for characterization and
analysis. Non-invasive imaging methods cannot reliably
differentiate reliably between coronary microvascular dysfunction
(MVD) and multi-vessel coronary artery disease (including left main
coronary artery disease; CAD) as both these conditions may result
in diffuse myocardial ischemia, which on visual and quantitative
analysis can have a similar appearance. Consequently, patients are
subjected to invasive angiography, and coronary microvascular
dysfunction is diagnosed after demonstrating normal coronary
arteries in patients with myocardial ischemia.
[0005] Analysis of first-pass enhancement images may result in true
quantification of the myocardial blood flow. While perfusion
deficits can be analyzed by true quantification of the myocardial
blood flow, non-invasive methods can, however, only assess the
distribution and severity of ischaemia, but they cannot measure the
spatio-temporal homogeneity of perfusion in different segments of
the myocardium. For instance, MVD and CAD are both characterized by
a severe and spatially widespread ischaemia, usually associated
with a delayed arrival of contrast agent to the endocardial layers
of the myocardium.
[0006] It is therefore an object of the invention to provide an
improved method of characterizing myocardial perfusion pathology by
analyzing a plurality of medical images of at least a portion of
the heart of a subject of interest, the plurality of medical images
being acquired in a consecutive manner by a medical imaging
modality.
[0007] This object is achieved by the method comprising the
following steps:
[0008] delineating contours of a selected part of the heart of the
subject of interest in the plurality of medical images and
segmenting the selected part into a plurality of segments;
[0009] sampling intensities of selected myocardial image positions
from the plurality of medical images and assigning an index
representing an order of acquisition of each one of the medical
images to the respective sampled intensities of the myocardial
image positions to obtain intensity curves for each of the selected
myocardial image positions;
[0010] calculating an index number indicative of a spatio-temporal
perfusion inhomogeneity or perfusion dephasing among at least a
subset of myocardial segments of the plurality of myocardial
segments, based on the obtained intensity curves.
[0011] The phrase "a selected part of the heart", as used in this
application, shall be understood particularly as any vascular
cavity of the heart, and shall also be understood to encompass the
left ventricle and the ascending aorta.
[0012] The phrase "medical imaging modality", as used in this
application, shall particularly encompass cardiac magnetic
resonance (CMR) imaging devices, cardiac computed tomography (CCT)
imaging devices, coronary angiography (CA) devices, CCT angiography
(CCTA) devices, intravascular ultrasound (IVUS) devices,
single-photon emission computed tomography (SPECT) devices,
positron emission tomography (PET) devices and echocardiography
devices.
[0013] The phrase "spatio-temporal perfusion inhomogeneity" may
also be referred to as "spatial-temporal dephasing" in this
application, and shall be understood particularly as the temporal
and spatial distribution of inhomogeneous myocardial blood flow in
case of a pathologic abnormality.
[0014] The step of delineating contours of the selected part of the
heart may be carried out manually, semi-automatically or fully
automatically. Appropriate segmentation techniques are known in the
art, commercially available and shall therefore not be discussed in
more detail herein.
[0015] The subset of myocardial segments may comprise a strict
subset of the plurality of myocardial segments like a perfusion
territory, or it may comprise the complete myocardium.
[0016] The index representing an order of acquisition of each one
of medical images may be referenced to a timescale, and may be time
itself.
[0017] One advantage of the method lies in the fact that additional
temporal information is provided on the distribution of perfusion
to different regions of the selected part of the heart that can be
used to characterize specific myocardial pathologies in a fast and
simple way. In particular, the calculated index number can be used
to distinguish coronary artery disease and microvascular disease in
a characterization.
[0018] Another advantage of the method is that the additional
information can be provided by a non-invasive method, so that an
invasive angiographic assessment can be avoided in many cases.
[0019] Prior to applying the step of delineating contours of the
selected part of the heart, the plurality of medical images may
have been subjected to an image registration technique to correct
for breathing motion of the subject of interest. Appropriate
registration techniques are well known in the art and shall
therefore not be discussed in detail herein.
[0020] Further, the obtained curves of intensity may have been
subjected to filtering for better result. Any filtering technique
that is suitable to the person skilled in the art may be
employed.
[0021] In a preferred embodiment, the method further comprises a
step of conducting quantification of myocardial blood flow in each
segment of the plurality of segments. The step of conducting true
quantification of myocardial blood flow may be carried out
according to one of the state-of-the-art techniques described in
the review article presented in the Background section, as for
instance a deconvolution method, or according to any other
technique that the person skilled in the art considers to be
suitable. The true quantification of myocardial blood flow in each
segment can provide complementary information for characterizing
myocardial perfusion pathology.
[0022] In another embodiment of the method, the plurality of
medical images is acquired by the medical imaging modality after
administering a contrast agent to the subject of interest. The
phrase "contrast agent", as used in this application, shall be
understood particularly as any agent that generates a larger signal
compared to a baseline when being acquired by the medical imaging
modality than the tissue of the subject of interest surrounding the
agent. If the medical imaging modality is based on a working
principle using gamma rays, the phrase "contrast agent" shall also
encompass radioactive tracer materials. In this way, a
signal-to-noise ratio can be improved and a more exact
characterization of myocardial fusion pathology can be
accomplished.
[0023] In one embodiment, the plurality of medical images may be
acquired after administering the contrast agent to the subject of
interest and during first-pass of the contrast agent through the
heart.
[0024] In another embodiment, the plurality of medical images may
be acquired after administering the contrast agent to the subject
of interest, and during a time when a concentration of the contrast
agent has reached a steady-state concentration in the subject of
interest. This is of special importance for acquiring medical
images by stress echo perfusion imaging.
[0025] In one embodiment, the plurality of medical images may be
acquired using endogenous contrast, like e.g. arterial spin
labeling, and during first-pass of the contrast agent through the
heart.
[0026] In another preferred embodiment, the method further
comprises a step of identifying a reference location in the
selected part of the heart, wherein in the step of calculating the
index number, the intensity curves are evaluated with reference to
a reference time that is determined by the identified reference
location. By that, a precise reference for calculating the index
number can be provided. A preferred reference location is the left
ventricle, as the left ventricle is the location that receives the
contrast agent during first-pass and precedes the upslope in the
obtained intensity curves for each of the selected myocardial image
positions. The phrase "upslope", as used in this application, shall
be understood particularly as a moment in time when an intensity of
the obtained intensity curves due to the administering of the
contrast agent exceeds a predetermined threshold, e.g. of 10%,
compared to an intensity without the contrast agent.
[0027] In another preferred embodiment, the method further
comprises a step of automatically determining, for each of the
selected myocardial positions, an individual time period relative
to a reference time that is determined by the identified reference
location until an occurrence of a characteristic feature of the
sampled intensity of each of the myocardial image positions. Then,
the individual time periods are used in the step of calculating the
index number. The characteristic feature may be a point in time of
onset of intensity rise, a point in time of peak intensity, or any
other characteristic feature that appear suitable to the person
skilled in the art. In this way, the index number indicative of the
spatio-temporal perfusion inhomogeneity can readily be calculated
in an automatic way.
[0028] Preferably, the step of calculating the index numbers
comprises a calculation of a statistical measure that is indicative
of a variation of the time until occurrence of the characteristic
feature at each of the individual myocardial positions relative to
the time of occurrence of the characteristic feature at the
identified reference location. By that, an index number can be
provided that describes the spatio-temporal perfusion inhomogeneity
among the myocardial segments in a very significant way. The
statistical measure may have the form of the variance, customarily
used in statistics as a measure of how far a set of numbers spreads
out. In this sense, the variance may be the square of the standard
deviation of the set of numbers. In general, the statistical
measure may have any other form that the person skilled in the art
considers suitable for indicating the variation of the time until
occurrence of the characteristic feature at each of the individual
myocardial positions.
[0029] Preferably, the acquiring of the plurality of medical images
of at least a portion of the heart of the subject of interest is at
least partially synchronized to a cyclic movement of the heart of
the subject of interest. For instance, a medical image can be
acquired at a fixed amount of time before or after a reference
event in the electrocardiogram like the R-peak of the QRS complex.
An advantage of this embodiment of the method is that all medical
images of the plurality of medical images are taken at a similar
status of the heart, so that there is little motion of the
myocardial ventricle among the medical images, and the myocardium
is rendered relatively stationary.
[0030] In yet another embodiment of the method, in the step of
sampling intensities of myocardial image positions, the myocardial
image positions are selected in a direction along the myocardium as
well as in a direction across the myocardium. In this way, the
calculated index number represents the spatio-temporal perfusion
inhomogeneity among the myocardial segments in an especially proper
way.
[0031] The method may further comprise a step of generating a
perfusogram and displaying it to a user. The phrase "perfusogram",
as used in this application, shall be understood particularly as a
color representation of the intensities of image positions in the
myocardium as a function of position and time. The horizontal axis
of the perfusogram may represent time and the vertical axis may
represent position (i.e. segment) in the myocardium. "Perfusograms"
has been described as a useful tool of visualizing myocardial
perfusion in publications earlier, for instance in: Marcel
Breeuwer, Comprehensive visualization of first-pass myocardial
perfusion: The uptake movie and the perfusogram", (International
Society for Magnetic Resonance in Medicine) ISMRM 2002. For
instance, the perfusogram may be displayed on a monitor unit that
is customary for the medical imaging modality the plurality of
medical images has been acquired with.
[0032] Furthermore, the method may preferably comprise a step of
implementing at least one marker in the perfusogram that is
indicative of at least one characteristic position and/or at least
one characteristic point in time. Examples of such markers that can
convey information contained in the perfusogram in a fast way to
the user are positions of the coronary artery perfusion
territories, borders of the segments of the left ventricle (for
instance, according to the AHA 17 segment model) and characteristic
moments in time of the passage of the contrast agent like time of
onset and time of peak. The marker may be formed as a straight
line, a curved line, or as a closed loop marking a territory of the
myocardium.
[0033] In another preferred embodiment, the method may further
comprise a step of implementing a plurality of computer links,
wherein each computer link of the plurality of computer links is
assigned to a location in the perfusogram, and wherein each
computer link of the plurality of computer links is linked to a
data set representing a medical image of the plurality of medical
images. In this way, detailed information on the myocardial blood
flow can be readily provided to the user, usually a medical staff
member.
[0034] It is another object of the invention to provide a system
for myocardial perfusion pathology characterization by analyzing a
plurality of medical images of at least a portion of the heart of a
subject of interest. The plurality of medical images is acquired in
a consecutive manner by a medical imaging modality. The system
comprises
[0035] a delineation unit, provided for delineating contours of a
selected part of the heart of the subject of interest in the
plurality of medical images and for segmenting the selected part
into a plurality of segments, and
[0036] an intensity sampler and analyzing unit.
[0037] The intensity sampler and analyzing unit is configured
[0038] for sampling intensities of myocardial image positions from
the plurality of medical images and assigning an index representing
an order of acquisition of each one of the medical images to the
respective sampled intensities of the myocardial image positions,
and
[0039] for calculating an index number indicative of a
spatio-temporal perfusion inhomogeneity or perfusion dephasing
among at least a subset of myocardial segments of the plurality of
myocardial segments. The system can provide the same advantages as
disclosed above for the method.
[0040] In another aspect of the invention, the system for
myocardial perfusion pathology characterization is an integral part
of the medical imaging modality that the plurality of medical
images has been acquired with. Preferably, the medical image
modality is designed as a magnetic resonance imaging apparatus. The
magnetic resonance imaging apparatus may advantageously comprise
synchronization means for synchronizing an acquiring of medical
images to a cyclic movement of the heart of the subject of
interest.
[0041] In yet another aspect of the present invention, a software
module is provided for carrying out an embodiment of any of the
methods of characterizing myocardial perfusion pathology disclosed
above or a combination thereof, wherein the method steps to be
conducted are converted into a program code of the software module,
wherein the program code is implementable in a memory unit of a
control unit of the medical imaging modality and is executable by a
processor unit of the control unit of the medical imaging
modality.
[0042] The control unit may be the control unit that is customary
for controlling functions of the medical imaging modality. The
control unit may alternatively be an additional control unit that
is especially assigned to execute the method steps.
[0043] The software module can enable a robust and reliable
execution of the method and can allow for a fast modification of
method steps and/or an adaptation of the image registration
algorithm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiments described
hereinafter.
[0045] In the drawings:
[0046] FIG. 1 is a schematic illustration of a part of an
embodiment of a medical imaging modality in accordance with the
invention, designed as a magnetic resonance imaging system;
[0047] FIG. 2 is a schematic illustration of intensity curves
obtained in accordance with the invention for myocardial perfusion
during first-pass of a contrast agent through the heart of the
control individual (top), through the heart of an individual having
a microvascular dysfunction (middle), and through the heart of an
individual with a three-vessel coronary artery disease
(bottom);
[0048] FIG. 3 shows diagrams comprising calculated index numbers
indicative of spatio-temporal perfusion inhomogeneity, calculated
from the intensity curves pursuant to FIG. 2; and
[0049] FIG. 4 illustrates an example of a perfusogram.
DETAILED DESCRIPTION OF EMBODIMENTS
[0050] FIG. 1 shows a schematic illustration of a part of an
embodiment of a medical imaging modality 10 in accordance with the
invention that is designed as a magnetic resonance imaging system,
for acquisition of medical images, represented by magnetic
resonance images, of at least a portion of the heart of a human
subject of interest 20. The magnetic resonance imaging system
comprises a magnetic resonance scanner 12 having a main magnet 14
provided for generating a static magnetic field. The main magnet 14
has a central bore that provides an examination space 16 around a
center axis 18 for the subject of interest 20 to be positioned
within. For clarity reasons, a conventional table for supporting
the subject of interest 20 has been omitted in FIG. 1. The
substantially static magnetic field defines an axial direction of
the examination space 16, aligned in parallel to the center axis
18. Further, the magnetic resonance imaging system 10 includes a
magnetic gradient coil system 22 provided for generating gradient
magnetic fields superimposed to the static magnetic field. The
magnetic gradient coil system 22 is concentrically arranged within
the bore of the main magnet 14, as is known in the art.
[0051] In principle, the invention is also applicable to any other
type of magnetic resonance imaging system providing an examination
region within a static magnetic field. Furthermore, it is
appreciated that the invention can be used with any other medical
imaging modality that is configured to acquire medical images of at
least a portion of the heart of the subject of interest. Examples
of medical imaging modalities that the invention can be applied to
are cardiac computed tomography (CCT) imaging devices, coronary
angiography (CA) devices, CCT angiography (CCTA) devices,
intravascular ultrasound (IVUS) devices, single-photon emission
computed tomography (SPECT) devices, positron emission tomography
(PET) devices and echocardiography devices.
[0052] Further, the magnetic resonance imaging system comprises a
radio frequency antenna designed as a whole-body coil 24 that is
provided for applying a radio frequency electromagnetic field to
the examination space 16 during radio frequency transmit phases to
excite nuclei of or within the subject of interest 20. The
whole-body coil 24 is also provided to receive magnetic resonance
signals from the excited nuclei of or within the subject of
interest 20 during radio frequency receive phases. In an
operational state of the magnetic resonance imaging system, radio
frequency transmit phases and radio frequency receive phases are
taking place in a consecutive manner. The whole-body coil 24 has a
center axis and, in the operational state, is arranged
concentrically within the bore of the main magnet 14 such that the
center axis of the whole-body coil 24 and the center axis 18 of the
magnetic resonance imaging system coincide. As is well known in the
art, a cylindrical metal radio frequency shield 26 is arranged
concentrically between the magnetic gradient coil system 22 and the
whole-body coil 24.
[0053] The magnetic resonance imaging system further includes a
control unit 28 provided for at least controlling functions of the
magnetic resonance scanner 12 and the magnetic gradient coil system
22. The control unit 28 comprises a customary monitor unit 36.
[0054] Furthermore, the magnetic resonance imaging system comprises
a radio frequency transmitter unit 30 that is connected to and
controlled by the control unit 28. The radio frequency transmitter
unit 30 is provided to feed radio frequency power of a magnetic
resonance radio frequency to the whole-body coil 24 via a radio
frequency switching unit 32 during the radio frequency transmit
phases. During radio frequency receive phases, the radio frequency
switching unit 32 directs the magnetic resonance signals from the
whole-body coil 24 to an image processing unit 36 residing in the
control unit 28. The image processing unit 34 is configured for
processing acquired magnetic resonance signals to generate a
magnetic resonance image of the portion of the subject of interest
20 from the acquired magnetic resonance signals. Many different
variations of this technique are well known to the person skilled
in the art, and thus need not be described in further detail
herein.
[0055] For the acquisition of magnetic resonance images of the
heart of the subject of interest 20, the magnetic resonance imaging
system comprises synchronization means for synchronizing an
acquiring of medical images to a cyclic movement of the heart of
the subject of interest. The synchronization means are formed as an
electrocardiogram device 38 and a synchronization unit 42.
[0056] The electrocardiogram device 38 is provided for taking
measurements of the electrocardiogram data of the heart of the
subject of interest 20. To this end, a plurality of electrodes 40
of the electrocardiogram device 38 may be arranged at the subject
of interest 20. Further, the electrocardiogram device 38 includes
means for filtering the electrocardiogram data to reduce artifacts
generated by magnetic gradient fields. Suitable filtering means are
known to the person skilled in the art and shall therefore not be
described in more detail herein.
[0057] The electrocardiogram device 38 is coupled to the
synchronization unit 42, which is configured for generating a
trigger signal 50 to trigger an acquisition period of acquiring
magnetic resonance signals from a detection of the R-peak of the
QRS complex of the heart activity. The synchronization unit 42, in
turn, is coupled to the control unit 28. The control unit 28 is
configured to be synchronized by the trigger signals 50 that are
provided by the synchronization unit 42 for a generation of control
signals for the magnetic gradient coil system 22 generating the
gradient magnetic fields. To this end, the control unit 28 is
configured to generate a plurality of sequences upon receiving the
trigger signals 50, each sequence comprising radio frequency fields
and magnetic gradient fields.
[0058] The medical imaging modality 10 comprises a system for
myocardial perfusion pathology characterization 52 by analyzing a
plurality of medical images of at least a portion of the heart of a
subject of interest 20. The system for myocardial perfusion
pathology characterization 52 resides within a housing of the
control unit 28 and comprises a delineation unit 54, a blood flow
analyzer 56 and an intensity sampler and analyzing unit 58. The
functions and interactions of these devices will be explained in
detail thereinafter.
[0059] In a consecutive manner, a plurality of medical images in
the form of magnetic resonance images of the heart of the subject
of interest 20 is acquired by the magnetic resonance imaging system
after administering a contrast agent to the subject of interest 20
during first-pass of the contrast agent through the heart of the
subject of interest 20. A plurality of medical images has been
acquired for three different subjects of interest: a control
individual, an individual with a three-vessel coronary artery
disease, and an individual having a microvascular dysfunction,
respectively. The acquiring of the plurality of medical images of
the heart of the subject of interest 20 has been synchronized to
the cyclic movement of the respective heart of the subject of
interest 20 as described above.
[0060] After the acquiring of each plurality of medical images of
the heart of the respective subject of interest 20, the medical
images are analyzed by an embodiment of a method of characterizing
myocardial perfusion pathology in accordance with the invention.
The method is described in detail in the following as being applied
to one plurality of medical images. It is understood that the
method is applied in the same way also to the other two pluralities
of medical images.
[0061] In order to be able to carry out the method, the system for
myocardial perfusion pathology characterization 52 comprises a
software module 48 (FIG. 1). The method steps to be conducted are
converted into a program code of the software module 48, wherein
the program code is implementable in a memory unit 44 of the system
for myocardial perfusion pathology characterization 52 and is
executable by a processor unit 46 of the system for myocardial
perfusion pathology characterization 52.
[0062] In a preparatory step, each medical image of the plurality
of medical images is submitted to an image registration
algorithm.
[0063] In the first step of the method, contours of the left
ventricle of the heart of the subject of interest 20 are delineated
in the plurality of medical images and the left ventricle is
segmented into a plurality of segments by the delineation unit 54
of the system for myocardial perfusion pathology characterization
52.
[0064] In the next step of the method, the blood flow analyzer 56
of the system for myocardial perfusion pathology characterization
52 conducts a true quantification of myocardial blood flow in each
segment of the plurality of segments.
[0065] Then, myocardial image positions are selected by the
intensity sampler and analyzing unit 58 of the system for
myocardial perfusion pathology characterization 52. The myocardial
image positions are selected in a direction along the myocardium as
well as in a direction across the myocardium. The intensity sampler
and analyzing unit 58 then samples intensities of the selected
myocardial image positions from the plurality of medical images and
assigns an index representing an order of acquisition formed by a
time of acquisition of each one of the medical images to the
respective sampled intensities of the myocardial image positions to
obtain intensity curves 60 over time for each of the selected
myocardial image positions.
[0066] The obtained intensity curves 60 over time for the three
different subject of interest are schematically shown in FIG. 2
(top: control individual, middle: individual having a microvascular
dysfunction (MVD), bottom: individual with a three vessel coronary
artery disease (CAD)).
[0067] For the intensity curves 60 over time in FIG. 2, in order to
provide for a suitable timescale, a reference location in the left
ventricle was identified by the intensity sampler and analyzing
unit 58. The reference location is a location first to receive the
contrast agent during first-pass of the contrast agent and precedes
an onset of rise of the intensities of the selected myocardial
image positions. The point in time of the onset of rise of the
intensity at the reference location serves as a reference time. The
intensity curves 60 over time are evaluated with reference to the
identified reference location and reference time.
[0068] In a next step of the method, for each of the selected
myocardial positions an individual time period relative to the
identified reference location and corresponding reference time is
automatically determined until an occurrence of a characteristic
feature in the sampled intensity curve 60 of each of the myocardial
image positions. In this embodiment, the characteristic feature is
a peak intensity of the intensity curve over time. The individual
time periods to peak intensity TTPI are used in a next step of
calculating an index number 64, 66.
[0069] In a following step of the method, the intensity sampler and
analyzing unit 58 calculates a first index number 64 which is
indicative of a spatio-temporal perfusion inhomogeneity or
dephasing among a subset of myocardial segments of the plurality of
myocardial segments, based on the obtained intensity curves 60 over
time.
[0070] The first index number 64 indicative of the temporal
dephasing of the left ventricular perfusion is calculated in a next
step as a variance of the time periods to peak intensity TTPI
between the reference time and the time until the occurrence of the
peak intensity of the intensity curves 60 over time. Herein, the
variance is understood to be the square of the standard deviation
of the time periods TTPI.
[0071] A second index number 66 indicative of the temporal
dephasing of the left ventricular perfusion is calculated as a
coefficient of variation of the time periods to peak intensity TTPI
between the reference time and the time until the occurrence of the
peak intensity of the intensity curves 60 over time.
[0072] The results for the calculated index number 64, 66 displayed
in FIG. 3 clearly show significant differences between the control
individual (CTRL, left column), the individual with a three vessel
coronary artery disease (CAD, center column), and the one having a
microvascular dysfunction (MVD, right column).
[0073] As becomes apparent from the intensity curves 60 over time
in FIG. 2, MVD and three-vessel CAD are both characterized by a
severe and spatially widespread ischaemia, usually associated with
a delayed arrival of contrast agent to the endocardial layers of
the myocardium. However, adding spatio-temporal dephasing analysis
can provide additional information on the temporal distribution of
perfusion to different regions of the left ventricle. FIG. 3 shows
that the calculated index number 64, 66 constitutes the main
difference between CAD and MVD due to the different underlying
pathophysiology and allows for a specific characterization.
[0074] In the individual with CAD, the spatio-temporal distribution
of myocardial blood flow in the myocardium is increasingly
inhomogeneous. In the individual with MVD instead, the pathologic
alteration involves the microscopic circulation and its interaction
in systole with myocardial contraction. In this case, perfusion to
the epicardial layer is unobstructed and very homogeneous. However,
there is a delay in the transmural propagation of the first-pass
wave. Similarly to CAD, this causes widespread ischaemia with
delayed intensity rise onset. However, this feature is homogeneous
in the temporal domain throughout the myocardium, allowing the
non-invasive differentiation between CAD and MVD.
[0075] In another step of the method, a perfusogram 62 is generated
and displayed to a user by the monitor unit 36. FIG. 4 illustrates
an example of a perfusogram 62 having a gray-scale or color-coding.
Markers like straight lines can be implemented in the perfusogram
62 (not shown) that are indicative of characteristic positions
and/or characteristic points in time. Other markers can be inserted
in the perfusogram 62 as well (not shown) that are formed as closed
loops, and that are indicative of a regime of time and space in
which the myocardium is less well perfused.
[0076] In yet another step of the method, a plurality of computer
links is implemented in the perfusogram 62. Each computer link of
the plurality of computer links is assigned to a location in the
perfusogram 62, and each computer link of the plurality of computer
links is linked to a data set representing a medical image of the
plurality of medical images The computer mouse cursor shown in FIG.
4 is pointing at a location of the perfusogram 62 that represents a
specific point in time and a specific location in the myocardium.
By clicking a mouse button, the computer link to the data set
representing the medical image corresponding to the point in time
and location of the myocardium is activated, and the medical image
is displayed on the monitor unit 36 of the magnetic resonance
imaging system.
[0077] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description are to be considered illustrative or exemplary and
not restrictive; the invention is not limited to the disclosed
embodiments. Other variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing
the claimed invention, from a study of the drawings, the
disclosure, and the appended claims. In the claims, the word
"comprising" does not exclude other elements or steps, and the
indefinite article "a" or "an" does not exclude a plurality. The
mere fact that certain measures are recited in mutually different
dependent claims does not indicate that a combination of these
measures cannot be used to advantage. Any reference signs in the
claims should not be construed as limiting the scope.
REFERENCE SYMBOL LIST
[0078] 10 medical imaging modality [0079] 12 magnetic resonance
scanner [0080] 14 main magnet [0081] 16 examination space [0082] 18
center axis [0083] 20 subject of interest [0084] 22 magnetic
gradient coil system [0085] 24 whole-body coil [0086] 26 radio
frequency shield [0087] 28 control unit [0088] 30 radio frequency
transmitter unit [0089] 32 radio frequency switching unit [0090] 34
image processing unit [0091] 36 monitor unit [0092] 38
electrocardiogram device [0093] 40 electrode [0094] 42
synchronization unit [0095] 44 memory unit [0096] 46 processor unit
[0097] 48 software module [0098] 50 trigger signal [0099] 52 system
for myocardial perfusion pathology characterization [0100] 54
delineation unit [0101] 56 blood flow analyzer [0102] 58 intensity
sampler and analyzing unit [0103] 60 intensity curve over time
[0104] 62 perfusogram [0105] 64 first index number [0106] 66 second
index number [0107] AIF arterial input function [0108] LV left
ventricle [0109] TTPI time to peak intensity
* * * * *